There is a growing need for a flat-panel display for use in a computer with a wide spreading use of information terminals. With further advancement of informatization, there are also increasing opportunities in which information, which has been conventionally provided by paper medium, is digitized. Particularly, the needs for an electronic paper or a digital paper have been recently increasing since they are thin and light weight mobile display media which can be easily held and carried (see Patent document 1, described below).
Generally, the display medium of a flat panel display device is formed by using an element such as a liquid crystal, an organic EL (organic electroluminescence) and an electrophoresis. In such display medium, a technology which uses an active drive element (TFT element) as an image drive element has become a mainstream to ensure a uniformity of the screen luminosity and a screen rewriting speed and so forth. For example, in the conventional display device for use in the computer, TFT elements are formed on a substrate wherein the liquid crystal element, the organic EL element or the like is sealed.
As a TFT element, semiconductors including a-Si (amorphous silicon) and p-Si (polysilicon) can be mainly used. These Si semiconductors (together with metal films, as necessary) are subjected to a multilayering process wherein each of a source electrode, a drain electrode and a gate electrode is sequentially stacked on the substrate, which leads to an achievement of the production of the TFT element.
Such method of manufacturing a TFT element using Si materials includes one or more steps with a high temperature, so that there is needed an additional restriction that the material of the substrate should resist a high process temperature. For this reason, it is required in practice to use a high heat-resistant glass substrate. In the meanwhile, it may also be possible to use a quartz substrate. However the quartz substrate is so expensive that an economical problem will arise when scaling up of the display panels. Therefore, the glass substrate is generally used as the substrate for forming such TFT elements.
However, when the thin display panel as described above is produced by using the conventionally known glass substrate, there is a possibility that such display panel will have a heavy weight, lack flexibility and break due to a shock when it is fallen down. These problems, which are attributable to the formation of a TFT element on the glass substrate, are so undesirable in light of the needs for a portable thin display having lighter weight with the advancement of informatization.
From the standpoint of obtaining a substrate having flexibility and light weight in order to meet the needs for a lightweight and thin display, there is developed a flexible semiconductor device wherein TFT elements are formed on a resin substrate (i.e., plastic substrate). For example, Patent document 2 (see below) discloses a technique in which a TFT element is firstly formed on a substrate (i.e., glass substrate) by a process which is almost the same as conventional process, and subsequently the TFT element is removed from the glass substrate so that it is transferred onto a resin substrate (i.e., plastic substrate). In this technique, the glass substrate wherein the TFT element is provided thereon is adhered to a resin substrate via a sealing layer (e.g., an acrylic resin layer), and subsequently the glass substrate is removed therefrom. In this way, the TFT element is transferred onto the resin substrate.
In the method for manufacturing a TFT element using such a transference process, there is, however, a problem associated with the removal of the substrate (i.e., glass substrate). In other words, it is necessary to perform an additional treatment to decrease the adhesion between the substrate and the TFT element upon the removing of the substrate from the resin substrate. Alternatively it is necessary to perform an additional treatment to form a peel layer between the substrate and the TFT element and thus also necessary to physically or chemically remove the peel layer afterward. These additional treatments can make the process complicated, which may cause a productivity problem.